Niche partitioning of hydrothermal vent fauna in the North Fiji Basin, Southwest Pacific inferred from stable isotopes

Energy sources and trophic interactions among vent fauna were investigated in deep-sea hydrothermal vents in the North Fiji Basin (NFB), Southwest Pacific, using stable sulfur, carbon, and nitrogen isotopes. A Bayesian isotope mixing model (MixSIAR) was used to quantify the proportions of energy sources for symbiont-bearing taxa. Based on these results, symbionts of host taxa such as the hairy snail Alviniconcha boucheti , black snail Ifremeria nautilei , and vent mussel Bathymodiolus sp. showed different carbon fixation pathways or nutrient preferences. We also observed niche partitioning among the omnivores by utilizing different resources or by occupying different microhabitats. For example, the squat lobster Munidopsis spp. occupied the bottom part of the chimney where dead shells were scattered around, as it was predatory to mussels. The scale worm Branchinotogluma segonzaci exploited energy from particulate organic matter or free-living bacteria on the chimney, whereas shrimp Rimicaris variabilis , which were clustered around I. nautilei and Echionelamus ohtai communities, had isotopic compositions similar to them. In contrast, limpets attached to I. nautilei did not share resources with snails and derived energy from mixed carbon sources. Among the vent fauna that we sampled, the crab was the top predator in the NFB, possibly consuming everything but with a lower preference for mussels. Overall, we found a non-overlapping diet or spatial niche of the vent fauna, with each taxon having a unique source or metabolism, or proportion. Such diversification in resource use may play an important role in sustaining the coexistence of species in a small area.